The pledges were revealed in a letter to Mr Robinson just days before the firm bought Nama's northern loan portfolio, Project Eagle, for £1.2bn.

A copy of the letter was supplied by Cerberus to the Stormont inquiry into the deal, which has heard claims of intended kickback payments for politicians and business figures. Among those alleged to have been in line for a payment was Mr Robinson, a claim firmly denied by the First Minister.

Cerberus has also denied any inappropriate payments.

The letter was sent to Mr Robinson a day before he held a meeting with former US Vice President Dan Quayle, who is now a senior figure with Cerberus, in March last year.

It was not copied to Deputy First Minister Martin McGuinness, who has said he was unaware of the meeting with Mr Quayle. Cerberus was selected by Nama as the winning bidder for the portfolio 10 days later.

The letter said: "Cerberus will release personal and corporate guarantees as a key part of consensual workout plans with corporate borrowers."

It also pledged to provide incentives to borrowers.

The letter was provided by Cerberus to its legal advisors Brown Rudnick on March 24, 2014 and was passed on to Mr Robinson ahead of the meeting between him and Mr Quayle.

The meeting was also attended by one of Mr Robinson's special advisers, the then Finance Minister Simon Hamilton, and Ian Coulter, the then managing partner of Belfast law firm Tughans.

Mr Robinson's office previously secured similar assurances from another bidder, investment firm Pimco. But Pimco pulled out of the process. Following the completion of the deal, a £7.5m success fee paid to Tughans, who acted as Brown Rudnick's local advisers, was diverted by Mr Coulter to an Isle of Man account.

Mr Coulter subsequently left the law firm, and the matter was referred to the Law Society of Northern Ireland, which launched an investigation. Mr Coulter has denied any wrongdoing and said he would explain the transfer to the appropriate authorities.

Political blogger Jamie Bryson alleged Mr Robinson and four others had been in line to receive the money. This has been denied by Mr Robinson.